This section provides background information related to the present disclosure which is not necessarily prior art.
Vehicle manufacturers in the past relied on two layers of foam and/or “shoddy” material built up for lightweight constructions, in thicknesses of approximately one-fourth inch to multiple inches, which were applied in a blanket form to cover surface areas of the vehicle, such as the engine firewall and transmission tunnel, to attenuate vehicle and road noise entering the vehicle passenger compartment. When fuel economy concerns were not as stringent and higher horsepower engines were used, the attenuation systems could be thicker, increasing both their weight and thereby their noise attenuation capability, without significant impact on vehicle performance. As vehicle mile-per-gallon fuel rates have increased and horsepower ratings have decreased, attenuation system weight allowances have necessarily decreased, forcing attenuation system manufacturers to use lighter weight materials. Attenuation system weight has subsequently decreased, but at a tradeoff with acoustic attenuation achieved. It has therefore become desirable to provide acoustic attenuation systems that provide attenuation levels similar to the prior thicker/heavier designs while providing the benefits of reduced weight.